1. Field of the Invention
The present invention relates to a spindle motor which causes a recording medium to rotate, and a recording and reproducing apparatus equipped with the same.
2. Description of the Related Art
Spindle motors are widely used for rotation of the recording medium in recording and reproducing apparatuses such as hard disk drives (hereafter abbreviated to “HDD”). In recent years, there has been a strong demand for increased capacity in HDD, and the recording density is increasing at the rate of 60% to approximately 100% every year. Along with the increase in recording density, the degree to which the HDD heads floats has dropped to 10 nm or less. However, when the amount of floating decreases, there is an increased possibility that the head will collide with the disk. Collisions between the head and disk lead directly to crashing of the disk; accordingly, in order to achieve an increase in the recording density, it is necessary to reduce the occurrence of collisions themselves. In order to reduce the occurrence of collisions, it is necessary to carefully devise the design of the air bearing surface of the slider on which the head is mounted; furthermore, it is necessary to achieve smoothing and increased precision of the disk that is mounted on the spindle motor.
Conventionally, in spindle motors used in HDD, the disk (one example of a recording medium) is secured to the disk-carrying surface (one example of a medium-carrying surface) of a rotor hub (one example of a rotor) by a clamper having spring properties (one example of a clamping member). In this case, if the precision of the disk-carrying surface is poor, the inner peripheral part of the disk may be deformed in the shape of a cup, and the outer peripheral side may be deformed with a waviness having higher secondary, tertiary, or other harmonic components. Especially in the case of small-size disks with a size of 2.5 inches or smaller, in spite of the fact that a thin disk is used, shock resistance is required in mobile applications; accordingly, a large clamping force is necessary. As a result, especially in small-size disks, deformation caused by clamping tends to occur.
In the past, therefore, spindle motors have been known in which a spiral shape cutting trace is formed so as to cover the entire circumference of the disk-carrying surface in order to reduce the deformation that is generated in the disk (for example, see Japanese Laid-Open Patent Application No. 2006-155864). In conventional spindle motors, turning is performed on the disk-carrying surface with the roughness profile set at a value that is rougher than values previously used. In concrete terms, the maximum height of the roughness profile Rz is set in the range of 0.8 μm to 6.3 μm, and the arithmetical mean deviation of roughness profile Ra is set in the range of 0.2 μm to 1.6 μm.
Furthermore, when the disk is fastened using the clamping member, a large load is placed on the rotor hub via the disk-carrying surface; accordingly, the rotor hub may undergo elastic deformation. When the rotor hub undergoes elastic deformation, the disk-carrying surface is inclined; as a result, the disk may be warped. In order to prevent this, a spindle motor is conventionally known in which the amount of deformation of the rotor hub is predicted in advance, and the disk-carrying surface is inclined so that this amount of deformation is canceled (for example, see Japanese Laid-Open Utility Model Application No. 05-059640).